The present invention is related to a rotor blade for a wind energy plant, with a blade root, with a first longitudinal portion starting from the blade root, with a second longitudinal portion, following up the first longitudinal portion and running into a blade tip, with a first surface, facing a tower of the wind energy plant in its assembled state, and a second surface, facing away from the tower of the wind energy plant in its assembled state, wherein an imaginary reference plane is spanned up by a rotation of the longitudinal axis of the first longitudinal portion around the rotational axis of a rotor of the wind energy plant carrying the rotor blade, which takes place in the operation of the rotor blade.
In addition, the present invention is related to a wind energy plant with a tower and a nacelle provided on the upper end of the tower, with a rotor, rotatably mounted around a rotational axis and having at least one rotor hub.
Rotor blades of modern wind energy plants have a considerable dimension, so that blades with a weight as small as possible are preferred in order to secure sufficient stability of the plant. This requirement has the result that the rotor blades have an elasticity which can lead to bending of the rotor blades in the operation of the plant, depending on the strength of the attacking wind.
In so-called front runner plants in particular, in which the wind meets first the rotor blades and then the tower of the plant, it has to be guaranteed even at bent rotor blades that the distance between blade tip and tower is sufficient. In order to make this sure, the distance between the rotor carrying the blades and the tower can be increased. Thus, the distance between the blade tips and the tower, the so-called tower freeway, is increased. This measure has several disadvantages, which make a correspondingly elaborate dimensioning of rotor and plant necessary.
For solving this problem, it is known from DE 298 80 145 U1, the entire contents of which is incorporated herein by reference, to form the rotor blades such that from the rotor hub towards the outside, they extend in a normal plane at first, and then, in a distance from the hub, in a curved manner, directed towards the outside and towards the front. As a result, this curved construction may be accompanied with cost-saving, because less stiffness is needed. Through this geometry of the rotor blades, a collision of the blade tips with the tower is to be safely avoided even in a strong wind, the rotor blades bending back to a straight course when they are loaded, but never coming too near to the tower. In this, the curvature of the rotor blades is provided in the outer region for aesthetic reasons, along the outer third of the blades, for instance.
From DE 201 20 324 U1, the entire contents of which is incorporated herein by reference, a rotor blade is known in which in the nonloaded state, the distance from the blade axis of those points of the blade bottom side pointing farthest towards upwind in the operation is at least as great as on the blade root on each position of the rotor blade. While the side of this rotor blade facing away from the tower in the operation is formed essentially straight, the side facing the tower in the operation has a curvature. Through this shape, a collision with the tower is to be excluded even at an extreme bending of the rotor blade due to wind.
Finally, in DE 10 2004 023 774 A1, the entire contents of which is incorporated herein by reference, a rotor blade is proposed which is disposed on the rotor hub aligned in an obtuse angle to the rotor rotational axis, tilted away from the tower (cone angle), and which is formed curved with respect to the longitudinal axis in at least one length portion. Through the combination of these two measures the disadvantages accompanied with the single use of the respective measures alone are to be avoided and a collision of the blade tips with the plant tower is to be excluded even in a strong wind. In the known rotor blade, the region of the blade tip can be formed straight again, after a region of curvature.
The rotor blades and wind energy plants known in the state of the art have the common disadvantage that due to the respective rotor blade geometry, the contour on the aerodynamically important suction surface of the blade (the side pointing towards the tower in front runners) can be formed accurately only with difficulty. This results in a reduced efficiency of the plants. In addition, in the rotor blades and wind energy plants known since a long time, high moments act around the blade longitudinal axis in the operation, and thus on the bearing of a possibly provided blade pitch control (compare DE 201 20 324 U1).
The present invention is based on the objective to provide a rotor blade and a wind energy plant of the kind mentioned in the beginning, which have an augmented efficiency and safely avoid collisions of the blade tip with the tower of the wind energy plant even in strong winds, and in which the moments around the longitudinal axis of the blade occurring in the operation are reduced.